Caramel color is a product of the heat treatment of carbohydrates, typically sugars, usually in the presence of a catalyst. There are several types of caramel colors, for example, non-acid resistant and acid resistant types. The different types of caramel colors are chosen for their suitability for a particular end use. With soft drinks, acid-resistant type caramel colors are required. Malt beverages such as beer require non-acid resistant caramel. Non-acid-resistant caramel color particularly suitable for malt beverages and which is salt stable is produced using an aqueous ammonia or anhydrous ammonia catalyst. This is referred to as ammonia caramel color.
Ammonia caramel color is generally produced using a batch type process. In a batch type process a large kettle containing up to 2000 gallons or more of a carbohydrate such as corn syrup is heated to boiling for about 8 to 12 hours. Gradually the ammonia catalyst is added and the color forms. This is then slowly cooled and filtered and brought to the desired concentration.
The batch process has several inherent problems. Since there is such a large mass of material, it is difficult to control the process conditions. The batch can burn and form an irreversible gelatinous mass which must be discarded and constitutes waste of the entire batch. Batch reactors also require a large capital investment to provide a reaction vessel suitable to hold such a large volume. Further the period of time required for a batch process is excessive.
This time period could be reduced by increasing the reaction temperature which will increase the reaction rate. In order to do this, however, increased pressure is required. Such increased pressure causes hazing of the caramel thereby providing an unacceptable caramel color.
A problem with caramel color is the production of 4-methyl imidazole (hereafter 4MeI) and 2-acetyl-4(5)-tetrahydroxy butyl imidazole (hereinafter THI). Over the past several years the Food and Drug Administration has limited the content of 4MeI in caramel color and THI content may soon be limited. It is believed that 4MeI and THI are reaction products of the carbohydrates in combination with the ammonia catalyst. To conduct the production of 4MeI and THI the ammonia catalyst must be added to the batch reactor very slowly. This is particularly difficult to control accurately; and even with this slow addition of the ammonia catalyst, unacceptably high levels of 4MeI and THI are sometimes encountered. Such high levels can require discarding of an entire batch of caramel color.
Although apparently never commercially developed, methods have been disclosed to produce caramel color in a continuous manner under high pressure. For example, Meisel U.S. Pat. No. 3,214,294 and Ackermann U.S. Pat. No. 3,385,733 disclose continuous methods of producing caramel colorings. The Ackermann reference teaches forming a mixture of catalyst and polysaccharide syrup preferably corn syrup, preheating this to a temperature of 350.degree. F. to 1,000.degree. F., maintaining this reaction mixture in a continuous reactor under pressure for a period of 5 to 300 minutes. Various catalysts including phosphoric and sulfuric acids and ammonium, potassium or sodium hydroxide are disclosed. Meisel also discloses using ammonium bisulfite as a catalyst. These methods are only for acid resistant caramel colors.
Ammonia caramel produced according to the teachings of Meisel or Ackermann would have excessively high 4MeI and THI contents and further hazing would occur causing an unacceptably cloudy product.